1. Field of the Invention
Stylographic or technical writing pens of the general type embodying an ink reservoir, and a tubular stylus or writing tip which is communicated to the reservoir, wherein a weighted cleaning wire is positioned within the reservoir for reciprocal cleaning movement within the writing tip. The improvements taught herein specifically relate to a new manner of designing venting channels for such a category of device, so that the pen point will not drip, in response to ever present ink contractions, and expansions, into the venting channel.
2. Description of the Prior Art
At the present time applicants are aware of numerous prior art teachings with respect to the design of a venting channel, i.e., expansion chamber, within an overall technical drafting pen design. An appreciation for the numerous, and disparate, prior art approaches to technical pen designs may be had by reference to the following Patent Nos.:
______________________________________ Federal Republic of Germany: Brossi AUS 1,259,733 (1968) Faber-Castell AUS 1,273,368 (1968) Kupferschmidt OFF 1,561,871 (1970) Riepe AUS 1,786,443 (1972) Riepe-Werke AUS 1,906,013 (1970) Riepe OFF 1,911,950 (1970) Riepe et al OFF 1,911,951 (1970) Gunter OFF 2,019,917 (1971) Riepe OFF 2,136,155 (1973) Riepe OFF 2,216,015 (1973) Arrasse OFF 2,460,345 (1975) France: Clement 986,766 (1951) Great Britain: Riepe 1,192,123 (1970) Riepe 1,192,124 (1970) United States: DeMarest 634,308 Wallace 1,524,068 Kovacs 2,401,167 Kovacs 2,891,512 Riepe 3,315,644 Gossel 3,418,058 Hebborn et al 3,442,597 Matschkal 3,459,486 Dahle 3,539,269 Danjzcek et al 3,741,668 Glasa et al 3,756,733 Glasa et al 3,788,754 Danjczek et al 3,824,023 Mutschler 3,870,421 ______________________________________
The large number of above-listed prior art teachings is a testimony to the lack of agreement, among technical pen designers, with respect to a overall pen design which will be serviceable in a drafting environment. This is a most crowded art, and a large number of the above-noted patents are owned by an affiliate of the assignee of the present application. While each of the above-identified prior art references is analogous art to the invention taught herein, none of the prior teachings, individually or collectively, is seen to be pertinent to the present teachings for a manner of pressure balancing a stylographic pen, through a parametrizing of certain critical geometrical relationships within the drafting pen itself. As has been noted hereinbefore, the prior art was completely ignorant of the approach taught herein, and the present invention is predicated upon the essential and inventive beginning of looking at the total pressure, at a pen point, with respect to the entire ink volume, including capillary effects. Applicants identified the problem of drip to be one which was inherent whenever a volume of ink were to be displaced, due to air expansion, and consequent movement into an expansion chamber, i.e., a venting channel. Applicants' novel approach was to create a structure which would inherently maintain a total pressure balance, so the pen tip would not drip, despite ink expansions and contractions. It was applicants who first identified the essential problem of pen dripping and related performance parameters to be located primarily in the venting channel, and thereafter the inventors invented a constant total pressure system, at the writing tip, by an exact design parametrization for the total pen, and particularly the venting channel. It is also only applicants who teach how to use the LaPlace equation in a manner which allows analytical designing of a pen, and a design which has been proven empirically.
A number of the above-noted prior art discusses that the cross-section of the venting channel could be changed, and in some cases increased, maintained as large as possible, or otherwise. For example Riepe AUS Pat. No. 1,786,443 (equivalent to Great Britain Pat. No. 1,192,124) is owned by a foreign affiliate of the present assignee, and was well-known to the inventors herein. Riepe AUS Pat. No. 1,786,443 specifically illustrates a double spiral channel (4, 4') with an interconnection channel (A), all for the clearly taught purpose of preventing loss of moisture from the ink, and to somewhat prevent ink loss upon shaking. Hence, Riepe AUS Pat. No. 1,786,443 represents a 1972 level of thinking that an ink equilization chamber must be as large as possible, and there is hardly any suggestion, let alone specific teaching, that a cross-sectional shape should be exactly varied as a function of its height above the point of interconnection of that venting channel to an ink reservoir. In striking contrast, the present invention offsets the increases in hydrostatic vented ink column pressures by exactly balancing this increase through a capillary pressure increase at the ink/air interface of that section within the venting channel, through a design criteria based upon the LaPlace equation.
Similarly, Riepe AUS Pat. No. 1,906,013 is not particularly concerned with any design constraints for a given helical shaped channel, rather, this patent focuses upon simply giving a given pitch to the vent channel, to compensate for the female screw threads which surround.
The U.S. patent in the name of Gossel, U.S. Pat. No. 3,418,058, is considered analogous to the present invention, insofar as he teaches, at column 2, lines 50+, that his vent channel, B, is "designed so that its cross-sectional area of flow gradually increases from its rear end toward its front end," and also since Gossel illustrates one form of insert that can be discarded and replaced with another, if cleaning is not to be done. As will become more apparent hereinbefore, Gossel's approach is entirely without appreciation that the value of any cross-section can control ink flow at the point. Gossel's stated purpose is merely to allow an easy removal of the insert, and his passage (e) is located far from the point, not close, as is preferably taught herein.
Kovacs, U.S. Pat. No. 2,401,167, illustrates a vent system having two interior helical ribs (5, 5'), which form helical venting channels, whrrein the lower end of the channel communicates with atmosphere and, again, an upper end vent hole into the ink supply. In this respect it is similar to the Gossel technique, and Kovacs' non-enabling teachings on the venting channel is simply that the venting channels "increase in depth from their inner ends to their outward ends."
Accordingly, it can be seen that there is no shortage of helical venting channel teachings in the prior art, and further reference may be had, for example, to the Dahle U.S. Pat. No. 3,539,269, or the German Pat. Nos. Riepe OFF 1,911,950 and Riepe-Werke OFF 2,136,155.
The preferred embodiment of the present invention, as taught hereinafter, employs a helical spiral technique for exactly varying a cross-sectional shape of a venting channel, as a function of its height above a particular, and low, point of communication into an ink reservoir. Nonetheless, the present invention does not require that the vent channel move in a helical fashion, only that its cross-sectional area be a direct function of that sectional height above the communication between the channel and the reservoir. Accordingly, the prior art patents above-discussed are, by contrast, a testimony to the unique departure of the present invention. For example, Kovacs U.S. Pat. No. 2,401,167 at FIG. 1, illustrates an ink reservoir, 4, and a venting channel, 6, which communicates to the upper end of the reservoir, through passage 7. It was characteristic, in the prior art, to always locate the vent hole at the top of the pen nib or ink reservoir, while the present invention teaches advantages to a minimized value for L.sub.2.
To summarize, the foregoing listed patents, suggest various and sundry ways of designing a vent channel, including varying the cross-sectional area of a given venting channel, according to all manner of thinking. However, and as will become more apparent hereinafter, none begin to suggest that a venting channel must be designed so that its cross-sectional area is varied as a direct function of the distance, of that cross-section, above the interconnection of the entire vent channel system and the ink reservoir which is being so vented. Moreover, the prior art includes no enabling disclosure as to how the LaPlace equation can be critically used to generate a design parametrization, so that any increase in gravitational pressures, as the result of an increasing column of ink in a vent channel, can be exactly offset by a vent channel which necessarily also exactly increases the capillary pressure upon the meniscus of that increasing ink column. Accordingly, and in complete distinction to the stated reasons for any given particular vent channel structure within the above-noted prior art teachings, applicants herein, first have taught, that a well behaved technical drafting pen can result if you structurally ensure that the total pressure at the writing tip remains a constant, despite variations in the level of an ink column within a venting channel. It is well known that atmospheric and temperature changes will constantly vary the level of ink in an expansion chamber, and only the present invention teaches that an exact total pressure balance of the pen tip is a possibility. More importantly, the applicants herein teach an exact manner of making a venting channel structure so as to ensure that total pressure balance.